Groot isn't such a good example. I've been a fan of pre-hero Marvels since I started collecting in the '70s and knew him as a character since then. He was revived in Hulk Annual #5 in '76, along with a group of other monsters, which was a blast for someone like me. I'll let Wikipedia fill in the rest:
"Groot first appeared in Tales to Astonish #13 (Nov. 1960), and was created by Stan Lee, Larry Lieber and Jack Kirby.[2] He appeared again in The Incredible Hulk vol. 2 Annual #5 (Oct. 1976), alongside five other monsters from Marvel's anthology horror comics of the late 1950s and early 1960s. In The Sensational Spider-Man #−1 (July 1997), Groot was featured in a nightmare of the young Peter Parker.
Groot reappeared in 2006 in the six-issue limited series Nick Fury's Howling Commandos, and appeared in the Annihilation: Conquest and Annihilation: Conquest – Star-Lord limited series. Groot went on to join the Guardians of the Galaxy in the series of the same name, and remained a fixture of the title until its cancellation with issue #25 in 2010. Groot appeared in its follow-up, the limited series The Thanos Imperative, and, alongside fellow Guardian Rocket Raccoon, Groot starred in backup features in Annihilators #1–4 (March–June 2011) and Annihilators: Earthfall #1–4 (Sept.–Dec. 2011)."
So, maybe he was a B-lister but he had much more than a one-time forgotten appearance and was a part of the Marvel universe.
Now, that's not to say I don't think movie hype isn't crazy. One that leaps to my mind is Marvel Spotlight #4. The first appearance of a book? The value has gone up because of a book?